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Provided is a wireless transmission system which can transmit data
accompanying video/audio by a different transmission method depending on
the characteristic of the data in a wireless transmission environment
where the transmission band is narrow and a transmission error is easily
caused. The wireless transmission system includes: a wireless receiver
(3) connected to a sink device (4); and a wireless transmitter (2)
connected to a source device (1). A wireless communication is performed
between the wireless receiver (3) and the wireless transmitter (2) so
that video and audio are outputted from the source device (1) to the sink
device (4). The wireless receiver (3) and/or the wireless transmitter (2)
categorizes the data accompanying the video and the audio in accordance
with the characteristic thereof and transmits the accompanying data by
using a different transmission method depending on the categorization.

1. A wireless transmission system comprising: a first wireless
communication device connected to a display device; and a second
communication device connected to a video output device, the wireless
transmission system outputting video and audio from the video output
device to the display device by performing wireless communication between
the first wireless communication device and the second wireless
communication device, wherein the first wireless communication device
and/or the second wireless communication device categorize associated
data associated with the video and audio depending on the characteristics
thereof and transmit the associated data in different transmission modes
for respective categories by wireless.

2. The wireless transmission system of claim 1, wherein the first
wireless communication device and/or the second wireless communication
device include buffers for each category of the associated data.

3. The wireless transmission system of claim 1, wherein the
presence/absence of retransmission and the presence/absence of
transmission order rearrangement are differentiated for the transmission
modes.

4. The wireless transmission system of claim 1, wherein the first
wireless communication device and/or the second wireless communication
device include a plurality of wired transmission lines depending on
characteristics of the associated data, and the first wireless
communication device and/or the second wireless communication device
categorize the associated data for each of the wired transmission lines.

5. The wireless transmission system of claim 4, wherein the first
wireless communication device and/or the second wireless communication
device categorize the plurality of the associated data based on header
information thereof when a plurality of associated data having different
characteristics is transmitted through one wired transmission line.

6. The wireless transmission system of claim 4, wherein the display
device is connected through HDMI to the first wireless communication
device and the video output device is connected through HDMI to the
second wireless communication device, a plurality of the wired
transmission lines are made up of a TMDS line, a CEC line, a DDC line,
and an HPD line of HDMI standard, the associated data includes DIP
transmitted through the TMDS line, a CEC message transmitted through the
CEC line, an HDCP authentication message transmitted through the DDC
line, and a hot plug signal transmitted through the HPD line, and the
categories are divided into a first type including the DIP, a second type
including the CEC message and the HDCP authentication message, and a
third type including the hot plug signal.

7. The wireless transmission system of claim 6, wherein with regard to
the DIP, the second wireless communication device categorizes data for
adjusting image quality or audio that changes during watching/listening
video and audio into the first type and data that changes at the time of
switching a video output source into the third type.

8. The wireless transmission system of claim 6, wherein the transmission
mode of the first type is a mode in which retransmission and transmission
order rearrangement are not performed, the transmission mode of the
second type is a mode in which retransmission is performed while
transmission order rearrangement is not performed, and the transmission
mode of the third type is a mode in which retransmission and transmission
order rearrangement are performed, and a mode for updating old associated
data before a change in state remaining in a buffer.

Description

TECHNICAL FIELD

[0001] The present invention relates to a wireless transmission system,
and, more particularly, to a wireless transmission system for wirelessly
connecting devices compatible with the HDMI standard, etc., to each
other.

BACKGROUND ART

[0002] Digital interfaces of the HDMI standard are widely used as those
for transmission of video/audio, etc. The HDMI standard is arranged for
AV (Audio Visual) devices by adding an audio transmission function and a
copyright protection function to the DVI (Digital Visual Interface)
standard which is a digital connection standard between a computer and a
display. In the case of the HDMI standard, image (video) data/audio data
are transmitted in a mode called TMDS (Transition Minimized Differential
Signaling).

[0003] The prescription of CEC has been added to the HDMI standards since
Version 1.2a (see, e.g., "Supplement 1 Consumer Electronics Control
(CEC)" of Nonpatent document 1). This CEC protocol is a control protocol
that performs control between devices connected through an HDMI cable.
The CEC protocol enables various controls based on unique physical and
logical addresses assigned to devices present on an HDMI network. For
example, if a user plays back an HDMI-connected DVD (Digital Versatile
Disc) player when watching digital broadcasting on a television
apparatus, the television apparatus automatically switches input terminal
from broadcast receiving terminal to a terminal connected to the DVD
player by itself. A menu manipulation displayed by the DVD player,
power-on/off, etc., can be performed using a remote controller of the
television apparatus.

[0004] Terms related to CEC are defined in Nonpatent document 1; those
having an HDMI input terminal are defined as sink devices; and those
having an HDMI output terminal to output an AV stream are defined as
source devices. Those defined as repeater devices have the HDMI input
terminal and output terminal to input/output an AV stream and behave as
both the sink device and the source device. The sink devices mainly
include displaying devices; examples of the source devices include STB
(Set Top Box), various players for DVD, BD (Blu-ray Disc), etc., and
various recorders for DVD, BD, etc.,; and examples of the repeaters
include an AV amplifier, etc.

[0005] The HDMI devices are configured to transmit AV streams and
associated data associated with the AV streams via one HDMI cable (see,
e.g., Patent Document 1). The associated data includes, for example, a
CEC message used for inter-device control and an authentication message
used for HDCP (High-bandwidth Digital Content Protection) authentication
and is mutually exchanged between devices in parallel with the
transmission. of AV streams.

[0008] It is recently attempted to wirelessly transmit video/audio and
associated data associated therewith between devices compatible with the
HDMI standard. Such a wireless transmission system uses limited resources
(including CPU, transmission band, etc.) of wireless transmitter/receiver
to execute a wireless transmission processing of video/audio and
associated data.

[0009] In the case of wireless transmission, a band is generally limited
and errors are often included due to wireless characteristics.
Particularly, because a band is preferentially assigned to video/audio,
only a narrow band is assigned to the associated data such as format
information and control information associated with video/audio,
resulting in higher probability of occurrence of transmission error.

[0010] Since all the associated data are conventionally equally handled
regardless of characteristics of the associated data, for example, the
associated data for which transmission rate is important and some data
dropouts are acceptable and the associated data for which transmission
rate is not so important but data dropouts are unacceptable are
transmitted in the same transmission mode and, therefore, it is
problematic that the efficiency deteriorates and that the associated data
cannot correctly be transmitted if an amount of data to be transmitted
increases or if a transmission error or data dropout occurs.

[0011] The present invention was conceived in view of the situations and
it is therefore an object of the present invention to provide a wireless
transmission system that enables associated data associated with
video/audio to be transmitted in different transmission modes depending
on the characteristics thereof in a wireless transmission environment
having a narrow transmission band and easily causing a transmission
error.

Means for Solving the Problems

[0012] To solve the above problems, a first technical means is a wireless
transmission system comprising a first wireless communication device
connected to a display device; and a second communication device
connected to a video output device, the wireless transmission system
outputting video and audio from the video output device to the display
device by performing wireless communication between the first wireless
communication device and the second wireless communication device,
wherein the first wireless communication device and/or the second
wireless communication device categorize associated data associated with
the video and audio depending on the characteristics thereof and transmit
the associated data in different transmission modes for respective
categories by wireless.

[0013] A second technical means is the wireless transmission system of the
first technical means, wherein the first wireless communication device
and/or the second wireless communication device include buffers for each
category of the associated data.

[0014] A third technical means is the wireless transmission system of the
first or second technical means, wherein the presence/absence of
retransmission and the presence/absence of transmission order
rearrangement are differentiated for the transmission modes.

[0015] A fourth technical means is the wireless transmission system of
anyone of the first to third technical means, wherein the first wireless
communication device and/or the second wireless communication device
include a plurality of wired transmission lines depending on
characteristics of the associated data, and the first wireless
communication device and/or the second wireless communication device
categorize the associated data for each of the wired transmission lines.

[0016] A fifth technical means is the wireless transmission system of the
fourth technical means, wherein the first wireless communication device
and/or the second wireless communication device categorize the plurality
of the associated data based on header information thereof when a
plurality of associated data having different characteristics is
transmitted through one wired transmission line.

[0017] A sixth technical means is the wireless transmission system of the
fourth or fifth technical means, wherein the display device is connected
through HDMI to the first wireless communication device and the video
output device is connected through HDMI to the second wireless
communication device, a plurality of the wired transmission lines are
made up of a TMDS line, a CEC line, a DDC line, and an HPD line of HDMI
standard, the associated data includes DIP transmitted through the TMDS
line, a CEC message transmitted through the CEC line, an HDCP
authentication message transmitted through the DDC line, and a hot plug
signal transmitted through the HPD line, and the categories are divided
into a first type including the DIP, a second type including the CEC
message and the HDCP authentication message, and a third type including
the hot plug signal.

[0018] A seventh technical means is the wireless transmission system of
the sixth technical means, wherein with regard to the DIP, the second
wireless communication device categorizes data for adjusting image
quality or audio that changes during watching/listening video and audio
into the first type and data that changes at the time of switching a
video output source into the third type.

[0019] An eighth technical means is the wireless transmission system of
the sixth or seventh technical means, wherein the transmission mode of
the first type is a mode in which retransmission and transmission order
rearrangement are not performed, the transmission mode of the second type
is a mode in which retransmission is performed while transmission order
rearrangement is not performed, and the transmission mode of the third
type is a mode in which retransmission and transmission order
rearrangement are performed, and a mode for updating old associated data
before a change in state remaining in a buffer.

Effect of the Invention

[0020] According to the present invention, since associated data
associated with video/audio can be transmitted in different transmission
modes depending on the characteristics thereof in a wireless transmission
environment having a narrow transmission band and easily causing a
transmission error, an amount of data to be transmitted can be reduced.
Even if a transmission error, a data dropout, etc., occur in the
associated data, the associated data can correctly be transmitted. The
associated data needed to be rapidly transmitted can preferentially be
transmitted.

BRIEF DESCRIPTION OF DRAWINGS

[0021] FIG. 1 is a block diagram of an exemplary configuration of a
wireless transmission system according to one embodiment of the present
invention.

[0022] FIG. 2 is a diagram of an example of a table that describes
categories of associated data and a transmission mode for each category.

[0023] FIG. 3 is a diagram for explaining an example of a wireless AV
transmission method used in the wireless transmission system according to
the present invention.

[0024] FIG. 4 is a diagram for explaining another example of the wireless
AV transmission method used in the wireless transmission system according
to the present invention.

[0025] FIG. 5 is a diagram for explaining further example of the wireless
AV transmission method used in the wireless transmission system according
to the present invention.

MODES FOR CARRYING OUT THE INVENTION

[0026] Preferred embodiments of a wireless transmission system of the
present invention will now be described with reference to the
accompanying drawings. Although the following embodiments are described
by exemplarily illustrating HDMI devices, the present invention is
applicable to wireless devices capable of transmitting video/audio and
associated data associated with the video/audio by wireless.

[0027] FIG. 1 is a block diagram of an exemplary configuration of the
wireless transmission system according to one embodiment of the present
invention. In FIG. 1, 1 denotes a source device corresponding to a video
output device; 2 denotes a wireless transmitter corresponding to a second
wireless communication device; 3 denotes a wireless receiver
corresponding to a first wireless communication device; and 4 denotes a
sink device corresponding to a display device. The wireless transmitter 2
and the wireless receiver 3 are wirelessly connected and one repeater
device is made up of the wireless transmitter 2 and the wireless receiver
3. This wireless transmission system includes the wireless receiver 3
connected through HDMI to the sink device 4 and the wireless transmitter
2 connected through HDMI to the source device 1 and is configured to
output video and audio from the source device 1 to the sink device 4 by
performing wireless communication between the wireless transmitter 2 and
the wireless receiver 3.

[0028] Although the first wireless communication device and the second
wireless communication device of the present invention are devices
capable of wireless transmission and reception, the first wireless
communication device and the second wireless communication device are
referred to as the wireless receiver 3 and the wireless transmitter 2,
respectively, for the convenience of description.

[0029] Transmission side devices made up of the source device 1 and the
wireless transmitter 2 will first be described.

[0030] The source device 1 may be any device capable of outputting video
and audio and may be a tuner device such as STB, various recorders and
players for BD, DVD, etc., and a game device, for example. Although the
source device 1 includes constituent elements for implementing functions
as a video output device, these elements will not be described.

[0031] In FIG. 1, the source device 1 includes an HDMI output portion 11
and is connected through HDMI to the wireless transmitter 2. The HDMI
output portion 11 is an HDMI I/F for connecting an HDMI cable. The HDMI
cable includes a CEC line that is a bidirectional bus for transmitting a
control signal (CEC message) common to the devices.

[0032] The HDMI cable also includes a TMDS line for transmitting streams
of video/audio signals that are digital signals in a differential manner,
a DDC (Display Data Channel) line utilized for transmitting EDID
(Extended Display Identification Data) and transmitting an authentication
message used for HDCP authentication, an HPD (Hot-Plug Detect) line for
transmitting a hot plug signal giving notification that a device is
detected, etc., in addition to the CEC line. The EDID includes
information about a type of signals processable by a displaying
apparatus, information such as resolution of a display panel, and
information such as a pixel clock, a horizontal effective period, and a
vertical effective period. The EDID is obtained from the video display
side (the sink device 4) by the video transmission side (the source
device 1) and the video transmission side transmits a video signal
adapted to the resolution of a display panel to be used (a display panel
of the sink device 4 in this example). The EDID of the sink device 4 may
be copied and stored in the wireless transmitter 2 and, in this case, the
source device 1 can access the wireless transmitter 2 to obtain the EDID
of the sink device 4.

[0033] The wireless transmitter 2 is mainly composed of a control portion
21, a wireless communication portion 22, and an HDMI input portion 23.
The HDMI input portion 23 is an HDMI I/F for connecting the HDMI cable
described above to achieve the HDMI connection with the source device 1
and is connected to the HDMI output portion 11 of the source device 1 via
the HDMI cable. The connection through the HDMI cable between the HDMI
output portion 11 and the HDMI input portion 23 enables the source device
1 and the wireless transmitter 2 to transmit/receive various messages
such as a CEC message and an authentication message.

[0034] The control portion 21 is made up of a first buffer 211, a second
buffer 212, a third buffer 213, an HDMI communication processing portion
214, and an HDMI control portion 215. The HDMI control portion 215 is
connected to the HDMI input portion 23 via an AV (video/audio) line and a
message line. The HDMI communication processing portion 214 is connected
to the wireless communication portion 22 via an AV line and a message
line. In this case, a transmission line of video/audio data is defined as
an AV line and a transmission line of other associated data (such as
messages and control information) is defined as a message line, instead
of classifications in HDMI by TMDS line, CEC line, DDC line, HPD line,
and the like.

[0035] The wireless communication portion 22 converts video, audio, and
messages obtained from the HDMI communication processing portion 214 into
a format that can be transmitted by wireless and transmits the converted
video, audio, and messages to the wireless receiver 3 by wireless.

[0036] Reception side devices made up of the sink device 4 and the
wireless receiver 3 will then be described.

[0037] The sink device 4 maybe any device capable of displaying video and
outputting audio and may be a monitor or a television device with a
tuner, for example. Although the sink device 4 includes constituent
elements for implementing functions as a display device, these elements
will not be described.

[0038] In FIG. 1, the sink device 4 includes an HDMI input portion 41 and
is connected through HDMI to the wireless receiver 3. The HDMI input
portion 41 is an HDMI I/F for connecting an HDMI cable. The HDMI input
portion 41 connects the lines (the CEC line, the TMDS line, the DDC line,
and the HPD line) included in the HDMI cable as is the case with the
source device 1.

[0039] The wireless receiver 3 is mainly composed of a control portion 31,
a wireless communication portion 32, and an HDMI output portion 33. The
HDMI output portion 33 is an HDMI I/F for connecting the HDMI cable
described above to achieve the HDMI connection with the sink device 4 and
is connected to the HDMI input portion 41 of the sink device 4 via the
HDMI cable. The connection through the HDMI cable between the HDMI input
portion 41 and the HDMI output portion 33 enables the sink device 4 and
the wireless receiver 3 to transmit/receive various messages such as a
CEC message and an authentication message.

[0040] The control portion 31 is made up of a first buffer 311, a second
buffer 312, a third buffer 313, an HDMI communication processing portion
314, and an HDMI control portion 315. The HDMI control portion 315 is
connected to the HDMI output portion 33 via an AV (video/audio) line and
a message line. The HDMI communication processing portion 314 is
connected to the wireless communication portion 32 via an AV line and a
message line.

[0041] A main characteristic of the present invention is to transmit
associated data associated with video/audio in different transmission
modes depending on the characteristics thereof in a wireless transmission
environment having a narrow transmission band and easily causing a
transmission error. In this regard, the control portion 21 included in
the wireless transmitter 2 and the control portion 31 included in the
wireless receiver 3 are configured to perform control such that the
associated data associated with video and audio are categorized depending
on the characteristics thereof to transmit the associated data in a
different transmission mode for each category by wireless. Specifically,
the control portion 21 and the control portion 31 provide the buffers
(the first buffer to the third buffer in this example) for respective
categories of the associated data and differentiate the presence/absence
of retransmission and the presence/absence of transmission order
rearrangement for the transmission modes of the associated data.

[0042] FIG. 2 is a diagram of an example of a table that describes
categories of associated data and a transmission mode for each category.
This table is stored in memories (not depicted) provided in the control
portion 21 and the control portion 31 and the HDMI control portion 215
and the HDMI control portion 315 refer to the table as needed. In this
example, the associated data is categorized into three types depending on
the characteristics thereof. The type 1 includes the data which needs a
high transmission rate but allows the certainty of transmission to be
low, and the transmission mode is represented as "retransmission: no" and
"transmission order rearrangement: no". The type 2 includes the data
which does not need a high transmission rate but needs a high certainty
of transmission (transmission is performed certainly in sequence), and
the transmission mode is represented as "retransmission: yes" and
"transmission order rearrangement: no". The type 3 includes the data
which does not need a high transmission rate but needs a high certainty
of transmission and allows the old data of the same kind remaining in a
queue (buffer) to be discarded since only the last value of continuously
updated data may be transmitted, and the transmission mode is represented
as "retransmission: yes" and "transmission order rearrangement: yes (old
information before change in state remaining in queue (FIFO) is
discarded)".

[0043] With respect to the criteria for determination of the types 1, 2,
and 3, for example, the associated data that changes in viewing video and
audio is categorized into the type 1; the associated data that relates to
commands or procedures for authentication is categorized into the type 2;
and the associated data that changes at the time of switching of a video
source such as switching into another source device is categorized into
the type 3.

[0044] Therefore, the data is categorized into the type 1 when the
transmission rate is important. The data categorized into type 1 is
repeatedly transmitted at regular intervals from the transmission side
regardless of the presence of change and no acknowledgement (ACK) is
returned from the reception side. After the data is received, a necessary
processing is performed on the reception side if a state has changed
based on the reception data. The data categorized into the type 1 has a
limited transmittable data amount and a higher update frequency at a
certain data rate and corresponds to state information that changes in
synchronization with video/audio such as sound volume (volume)
information and audio/video mute control information included in DIP
(Data Island Packet), for example.

[0045] The data is categorized into the type 2 when the transmission rate
is not important and the data must entirely be transmitted. The data is
stored in a queue (FIFO) on the transmission side and transmitted in
sequence when the transmission can be performed, and if no
acknowledgement (ACK) is returned from the reception side, the
corresponding and subsequent data are retransmitted. After the data is
received, ACK is returned from the reception side to the transmission
side and processing that corresponds to the received data is executed.
The data categorized into the type 2 does not permit the rearrangement of
the order and a data dropout and includes a CEC message (CEC), an HDCP
authentication message, EDID (DDC), and wireless communication control
information between a wireless transmitter and a wireless receiver, for
example. However, EDID is device information and basically unchanged and
therefore may be categorized into the type 3.

[0046] The data is categorized into the type 3 when the transmission rate
is not important and only a notification of state is necessary. As is the
case with the type 2, the data is stored in a queue (FIFO) on the
transmission side and transmitted in sequence when the transmission can
be performed, and if no acknowledgement (ACK) is returned from the
reception side, the corresponding and subsequent data are retransmitted.
A difference from the type 2 is in that if data of the same kind already
exists in a queue on the transmission side, old data is replaced with new
data and the old data is discarded. After the data is received, ACK is
returned from the reception side to the transmission side and processing
that corresponds to the received data is executed. Although ACK and
retransmission are necessary as is the case with the type 2, when a video
source is switched and data is changed, the data of the same kind not
completely transmitted is always overwritten and discarded and,
therefore, an overall data transmission amount is reduced as compared to
the type 2. The type 3 includes video/audio format information, light
control information, color correction information (DIP), and a hot plug
signal (HPD), for example. DIP is information that is periodically
transmitted regardless of the presence of change in HDMI as is the case
with the type 1 and, if a state is retained on the transmission side and
the reception side and only a changing point is transmitted as the type
3, a communication amount through a wireless section can considerably be
reduced.

[0047] Types of categories will hereinafter specifically be described for
associated data (messages) transmitted through the CEC line, the TMDS
line, the DDC line, and the HPD line of HDMI.

[0048] The CEC line is used for transmitting CEC messages that are various
control commands used for device coordination of HDMI (e.g., remote
controller signals, power on/off signals, and input switch signals) and
CEC messages for transmitting information specific to devices, for
example, information of reception strength in the case of the wireless
mode. Since the transmission must be performed certainly in sequence,
these messages are categorized into the type 2.

[0049] The wireless transmitter and the wireless receiver exchange the
wireless communication control information and the statuses of the
transmitter and the receiver as well as various parameters of reception
electric power, quality, etc., for the wireless control. These pieces of
information are categorized in to the type 2 since the wireless
communication between the transmitter and the receiver is mismatched
unless the transmission is performed in sequence.

[0050] The TMDS line is used for transmitting video/audio and DIP. Audio
and DIP are transmitted during a blanking period of video. The DIP mainly
transmits data associated with video/audio such as resolution information
and content protection information, can transmit a vendor-defined frame,
and can also transmit average brightness information, audio parameters,
etc. If DIP is set to a register at the implementation level on the
transmission side, the DIP is transmitted for each frame and can be read
out on the reception side when the DIP arrives.

[0051] There are two main types of DIP (the types 1 and 3) from the
characteristics of data. For example, backlight control information
(information or a control value of brightness for controlling backlight),
image quality adjustment processing information (such as OSD display
state), audio/video mute control information, sound volume information,
and audio valid/invalid information of HDMI (information for preventing
abnormal noise from occurring in an invalid section) are categorized into
the type 1 because a delay of the transmission affects viewing. For
example, a product ID and Vendor InforFrame (information dependent on a
vendor and not changed) are device information and not changed after
connection and are therefore categorized into the type 3, and
valid/invalid information of video signals, information related to video
adjustment, information related to resolution, content protection
information of audio, and color space information are also categorized
into the type 3 because these pieces of information are changed at the
timing of switching the video source and are not always continuously
changed.

[0052] The audio valid/invalid information of HDMI and the valid/invalid
information of video signals are pieces of information indicative of the
valid/invalid states of video and audio output from the transmission
side. Therefore, when an invalid signal is received from the transmission
side, these pieces of information are used for ignoring the signal on the
reception side and this prevents screen disturbance and abnormal noise
from occurring due to display/audio output based on invalid data.

[0053] The DDC line is used for transmitting EDID and the HDCP
authentication message. EDID is device information related to
specifications such as information of a format displayable on a display
device, is not changed after connection although the transmission must
certainly be performed, and is therefore categorized into the type 2 or
type 3. The HDCP authentication message is used for exchanging key
information in accordance with an authentication sequence based on a
protocol having a predetermined procedure, must be transmitted certainly
in sequence, and is therefore categorized into the type 2.

[0054] The HPD line is used for transmitting the hot plug signal. The hot
plug signal gives notification that a device is detected, and is
categorized into the type 3 since only the latest state may certainly be
transmitted.

[0055] The wireless transmitter 2 and the wireless receiver 3 include a
plurality of wired transmission lines (the CEC line, the TMDS line, the
DDC line, and the HPD line) corresponding to the characteristics of the
associated data. In a method of categorizing the associated data by the
wireless transmitter 2 and the wireless receiver 3, the associated data
can be categorized for each wired transmission line. If a plurality of
the associated data having difference characteristics is transmitted
through one wired transmission line, the associated data can be
categorized based on the header information thereof.

[0056] The associated data includes DIP transmitted through the TMDS line,
the CEC message transmitted through the CEC line, EDID and the HDCP
authentication message transmitted through the DDC line, and the hot plug
signal transmitted through the HPD line and is categorized into the type
1 (first type) including DIP, the type 2 (second type) including the CEC
message, EDID, and the HDCP authentication message, and the type 3 (third
type) including the hot plug signal. With regard to DIP, the data for
adjusting image quality or audio changed during watching/listening video
and audio is categorized into the type 1 and the data changed at the time
of switching a video output source is categorized into the type 3. The
EDID may be categorized into the type 3.

[0057] In FIG. 1, in the wireless transmitter 2, the HDMI control portion
215 categorizes the associated data input from the HDMI input portion 23
based on the transmission line, the header information, and the table
depicted in FIG. 2, stores the associated data categorized into the type
1 in the first buffer 211, stores the associated data categorized into
the type 2 in the second buffer 212, and stores the associated data
categorized into the type 3 in the third buffer 213. When transmitting
the associated data stored in the buffers to the wireless receiver 3 by
wireless, the HDMI communication processing portion 214 may add type
identification information for identifying the type to the header etc.,
of the associated data. When receiving the associated data from the
wireless transmitter 2, the wireless receiver 3 stores the associated
data of the type 1 into the first buffer 311, stores the associated data
of the type 2 into the second buffer 312, and stores the associated data
of the type 3 into the third buffer 313, based on the type identification
information added to the header. If the type 2 and the type 3 are
implemented such that the difference only exits in handling of a queue at
the time of transmission, a reception buffer can be shared between the
type 2 and the type 3 on the reception side.

[0058] In this way, the wireless transmitter 2 executes a transmission
processing in accordance with a protocol corresponding to the type and
the wireless receiver 3 executes a reception processing in accordance
with a protocol corresponding to the type.

[0059] Although the description has been made of the case that the
associated data is wirelessly transmitted from the wireless transmitter 2
to the wireless receiver 3 in the example, EDID is data transmitted from
the wireless receiver 3 to the wireless transmitter 2 by wireless, and
the CEC message is mutually exchanged between the wireless receiver 3 and
the wireless transmitter 2, for example. Therefore, the same processing
can obviously be executed in the case of transmitting the associated data
from the wireless receiver 3 to the wireless transmitter 2 by wireless.
The transmission channels provided by these protocols can also be used
not only for the associated data of connected HDMI but also for
categorizing communication of control information between wireless
devices in the same way.

[0060] FIG. 3 is a diagram for explaining an example of a wireless AV
transmission method used in the wireless transmission system according to
the present invention. This example explains a sequence example when the
associated data (hereinafter, a message) of the type 1 is transmitted by
wireless based on the system configuration of FIG. 1. On the transmission
side, the first buffer 211 stores "A, B, C, D" as a message of the type
1. The HDMI communication processing portion 214 reads the message "A, B,
C, D" from the first buffer 211 and the wireless communication portion 22
periodically wirelessly transmits this message to the wireless receiver
3. The message received from the transmission side is compared with a
message of the type 1 stored in the first buffer 311 on the reception
side and, if not changed, the message in the first buffer 311 is retained
without change.

[0061] In the wireless transmitter 2, when receiving a message categorized
into the type 1 from the source device 1 (S1), the HDMI control portion
215 identifies and rewrites a relevant message of the same kind in the
message "A, B, C, D" stored in the first buffer 211 (S2). In this
example, it is assumed that data "C" is rewritten into data "E". The HDMI
communication processing portion 214 reads a message "A, B, E, D" from
the first buffer 211 (S3) and the wireless communication portion 22
periodically transmits this message to the wireless receiver 3 by
wireless.

[0062] In the wireless receiver 3, the HDMI communication processing
portion 314 receives through the wireless communication portion 32 the
message "A, B, E, D" transmitted from the wireless transmitter 2 (S4),
and the HDMI communication processing portion 314 compares the message
received from the wireless transmitter 2 with a message stored in the
first buffer 311 and updates the message if change exists (S5). In this
example, since the message "A, B, E, D" is received from the wireless
transmitter 2 and the message stored in the first buffer 311 is "A, B, C,
D", the message has been changed and, therefore, the contents of the
first buffer 311 are updated. The HDMI control portion 315 transmits the
message "A, B, E, D" updated/stored in the first buffer 311 via the HDMI
output portion 33 to the sink device 4 (S6).

[0063] If a message that is transmitted by wireless from the transmission
side does not reach the reception side, the buffer on the reception side
is not updated in this example; however, the transmission is performed
regardless of the presence of change and, therefore, the both buffers are
synchronized when the message arrives next time.

[0064] FIG. 4 is a diagram for explaining another example of the wireless
AV transmission method used in the wireless transmission system according
to the present invention. This example explains a sequence example when
messages of the type 2 are wirelessly transmitted based on the system
configuration of FIG. 1. In this example, it is assumed that the first to
third buffers included in the wireless transmitter 2 and the wireless
receiver 3 are FIFO buffers.

[0065] In the wireless transmitter 2, when receiving messages A, B
categorized into the type 2 in series from the source device 1 (S11), the
HDMI control portion 215 adds these messages A, B into the second buffer
212 in the order of reception (S12). The HDMI communication processing
portion 214 reads the earlier received message A from the second buffer
212 (S13) and the wireless communication portion 22 wirelessly transmits
this message A to the wireless receiver 3.

[0066] In the wireless receiver 3, the HDMI communication processing
portion 314 receives through the wireless communication portion 32 the
message A transmitted from the wireless transmitter 2 (S14), and the HDMI
communication processing portion 314 stores the message A received from
the wireless transmitter 2 into the second buffer 312 and transmits "ACK"
for the message A by wireless to the wireless transmitter 2. The HDMI
control portion 315 transmits the message A stored in the second buffer
312 via the HDMI output portion 33 to the sink device 4 (S15).

[0067] In the wireless transmitter 2, when receiving via the wireless
communication portion 22 the "ACK" transmitted from the wireless receiver
3, the HDMI communication processing portion 214 determines that the
transmission of the message A is completed, and clears the message A
stored in the second buffer 212 (S16).

[0068] The HDMI communication processing portion 214 reads the message B
from the second buffer 212 and the wireless communication portion 22
transmits this message B by wireless to the wireless receiver 3. If
determining that "ACK" for the message B is not received from the
wireless receiver 3 for a certain period, for example, if the message B
does not reach the reception side or if an error occurs and the message B
is discarded on the reception side, the HDMI communication processing
portion 214 determines that a time-out occurs, and reads the message B
again from the second buffer 212 to retransmit the message B to the
wireless receiver 3 (S17).

[0069] As is the case with the message A, in the wireless receiver 3, the
HDMI communication processing portion 314 receives through the wireless
communication portion 32 the message B transmitted from the wireless
transmitter 2 and the HDMI communication processing portion 314 stores
the message B received from the wireless transmitter 2 into the second
buffer 312 and transmits "ACK" for the message B by wireless to the
wireless transmitter 2. The HDMI control portion 315 transmits the
message B stored in the second buffer 312 via the HDMI output portion 33
to the sink device 4.

[0070] In the wireless transmitter 2, when receiving via the wireless
communication portion 22 the "ACK" transmitted from the wireless receiver
3, the HDMI communication processing portion 214 determines that the
transmission of the message B is completed, and clears the message B
stored in the second buffer 212. ACK may be implemented as an independent
message or may be transmitted in association with a real communication
message for the sake of efficiency. ACK may be implemented so as to
correspond one-to-one to a message, or may be implemented such that one
ACK can serve as ACK for a plurality of messages.

[0071] FIG. 5 is a diagram for explaining further example of the wireless
AV transmission method used in the wireless transmission system according
to the present invention. This example explains a sequence example when
messages of the type 3 are transmitted by wireless based on the system
configuration of FIG. 1. It is assumed that the first to third buffers
included in the wireless transmitter 2 and the wireless receiver 3 are
FIFO buffers.

[0072] In the wireless transmitter 2, when receiving messages A, B, C
categorized into the type 3 in series from the source device 1 (S21), the
HDMI control portion 215 adds these messages A, B, C to the third buffer
213 in the order of reception (S22). The HDMI communication processing
portion 214 reads the earlier received message A from the third buffer
213 (S23) and the wireless communication portion 22 wirelessly transmits
this message A to the wireless receiver 3.

[0073] In the wireless receiver 3, the HDMI communication processing
portion 314 receives through the wireless communication portion 32 the
message A transmitted from the wireless transmitter 2 (S24), and the HDMI
communication processing portion 314 stores the message A received from
the wireless transmitter 2 into the third buffer 313 and wirelessly
transmits "ACK" for the message A to the wireless transmitter 2. The HDMI
control portion 315 transmits the message A stored in the third buffer
313 via the HDMI output portion 33 to the sink device 4 (S25).

[0074] In the wireless transmitter 2, when receiving via the wireless
communication portion 22 the "ACK" transmitted from the wireless receiver
3, the HDMI communication processing portion 214 determines that the
transmission of the message A is completed, and clears the message A
stored in the third buffer 213 (S26). The HDMI communication processing
portion 214 reads the message B from the third buffer 213 and the
wireless communication portion 22 transmits this message B by wireless to
the wireless receiver 3. If determining that "ACK" for the message B is
not received from the wireless receiver 3 for a certain period, the HDMI
communication processing portion 214 determines that a time-out occurs.
For example, if the HDMI control portion 215 receives a message B' of the
same kind as the message B categorized into the type 3 from the source
device 1 during the time-out determination period (S27), the message B
stored in the third buffer 213 (not cleared because of unreceived "ACK")
is rewritten into the new message B'.

[0075] The HDMI communication processing portion 214 reads the message B'
from the third buffer 213, and the wireless communication portion 22
transmits this message B' by wireless to the wireless receiver 3.

[0076] As is the case with the message A, in the wireless receiver 3, the
HDMI communication processing portion 314 receives through the wireless
communication portion 32 the message B' transmitted from the wireless
transmitter 2 and the HDMI communication processing portion 314 stores
the message B' received from the wireless transmitter 2 into the third
buffer 313 and wirelessly transmits "ACK" for the message B' to the
wireless transmitter 2. The HDMI control portion 315 transmits the
message B' stored in the third buffer 313 via the HDMI output portion 33
to the sink device 4.

[0077] In the wireless transmitter 2, when receiving via the wireless
communication portion 22 the "ACK" transmitted from the wireless receiver
3, the HDMI communication processing portion 214 determines that the
transmission of the message B' is completed, and clears the message B'
stored in the third buffer 213.

[0078] Although the update of the message B' has a risk of clearing the
message B' due to the ACK for the message B, the loss of data can be
prevented by the implementations such as using information associated
with the ACK to allow determination of data to which the ACK corresponds
or, more simply, dividing a queue to a transmission processing waiting
area and an ACK waiting area (an area for waiting the clearing due to ACK
after the transmission processing is executed once) and limiting the
overwrite to the transmission processing waiting area.

[0079] In the case of the messages categorized into the type 3, a message
of the same kind not completely transmitted is directly overwritten
unlike the type 2 and, therefore, the old message does not need to be
transmitted, thereby reducing a data transmission amount.

[0080] According to the present invention, since the associated data
associated with video/audio can be transmitted in different transmission
modes depending on the characteristics thereof in a wireless transmission
environment having a narrow transmission band and easily causing a
transmission error, an amount of data to be transmitted can be reduced.
Even if a transmission error, a data dropout, etc., occur in the
associated data, the associated data can correctly be transmitted. The
associated data needed to be rapidly transmitted can preferentially be
transmitted.

[0081] Since the associated data can be transmitted by using the wireless
channel same as the transmission of video and audio, another wireless
channel does not need to be added for sending the associated data.
Therefore, an antenna, an amplifier, a signal processing portion, etc.,
are unnecessary for realizing an additional wireless channel and cost
reduction can be achieved.

[0082] The wireless transmission utilizes a wireless frequency band (5-GHz
band) available without the need to obtain a license. Ranges of available
frequencies are regulated by law and another wireless device (such as
wireless LAN) utilizing the same frequency band (5-GHz band) is arranged
to perform communication by searching an unused frequency range
(frequency channel) through which no communication is performed.
According to the wireless AV transmission method of the present
invention, it is not necessary to add frequency range (frequency channel)
to be used and, therefore, a frequency range available to another
communication device accordingly increases, thereby increasing
opportunities for communication.